Broad-band antenna system



Jan. l, i952 F. A. KoLsTL-:R

BROAD BAND ANTENNA SYSTEM 4 Sheets-Sheetl l Filed May 22, 1947 www/WM AT TORNEVS Jam L 1952 F. A. KoLs'rER BROAD BAND ANTENNA SYSTEM 4Sheets-Sheet 2 Filed May 22, 1947 Jam 1 1952 F. A. KoLsTER BROAD BANDANTENNA SYSTEM Filed May 22, 1947 4 Sheets-Sheet 5 ATTORNEYS @wwf JanH952 F. A. KOLSTER 2,580,798 l BROAD BAND lANTENNA SYSTEM Filed May 22,1947 4 Sheets-Sheet 4 wwm ATTORNEYS Patented Jan. 1, 1952 UNITED STATESPATENT QFFICE BROAD-BAND ANTENNA SYSTEM Frederick A. Kolster, SanFrancisco, Calif.; Muriel Kolster administratrix of said Frederick A.

Kolster, deceased Application May 22, 1947, Serial No. 749,699

(Cl. Z50-33.59)

15 Claims.

This invention relates to particularly to antenna systems suited forefiicent operation throughout, or anywhere within,

`a wide band of frequencies.

Generally in accordance with the invention, to provide an antenna systemeniciently operative throughout a wide band of frequencies or at anyfrequency within a wide band, there are utilized two or more low Qdipoles of substantially different length so coupled that their netreactance as seen by the associated transmission line is low at allfrequencies within that band.

More specifically, the self and mutual impedances of the dipoleseffectively form a band-pass network which when reduced to its simpleequivalent series circuit for each frequency of the band appears to thetransmission line as a low reactance in series with a resistance of suchmagnitude that for all frequencies of .the band the impedances of theantenna and line are suitably matched to insure alow standing Waveratio. Further in accordance with the invention, the shorter dipolecontrols the amplitude and phase of current in the longer dipole,particularly at and near the harmonic frequencies thereof, to preventoccurrence of undesirable nulls in the field pattern of the antenna andso insure that throughout the wide frequency coverage of the antenna italways favors, or nowhere discriminates against, reception ortransmission in the desired direction.

The invention further resides in features of construction and operationhereinafter described and claimed.

For an understanding of the invention and for illustration ofembodiments thereof, reference is made to the accompanying drawings, inwhich:

Fig. 1, partly in section, illustrates one form ofbroad-band antenna;

Fig. 2 is al sectional view taken on line 2-2 of Fig, 1;

Fig. 3is a frequency versus standing-waveratio curve discussed inconnection with Fig. 1;

Fig. 4 comprises frequency versus reactance curves discussed inconnection with Fig. l;

Fig. 5 graphically represents modification of the antenna characteristicby addition of loading inductance;

Fig. 6 is a perspective view of another broadband antenna embodying theinvention;

Fig. 6A is an explanatory gure referred to in discussion of Figs'. 6 and8;

Fig. 7, in perspective and on enlarged scale, shows constructionaldetails of the antenna of Fig. 6; l

antenna systems, and

Fig. 8 is an elevational view of. a further modified form of broad-bandantenna;

Fig. 9 is a complex network referred to in discussion of Figs. 6 to 8;

Fig. 10 represents the series circuit equivalent of Fig. 9;

Fig. 11 is an explanatory figure referred to in discussion of thereactance-frequency and resistance-frequency characteristics of theantennae of Figs. 6 to 8 Figs. 12 to 15 are frequency versusstandingwave-ratio curves discussed in connection with Figs. 6 to 8; and

Fig. 16 comprises eld patterns discussed in connection with the antennasof Figs. 6 to 8. .Y

In the embodiment of the invention shown in Figs. 1 and 2, the dipole I0consists of two antenna elements I2 and I4 supported by tube I6 ofsuitable insulating material. The antenna elements are conductivelyconnected to the associated receiving or transmitting apparatus by atransmission line I8 which may be, as shown, a concentric lineconsisting of an inner conductor 20 and an outer conductor 22respectively con-l nected to the adjacent ends of the antenna elementsI2, I4.

Preferably and for reasons later discussed, an inductance 24 isconnected in parallel with the transmission line at its antennatermination. The antenna may, however, be used without such inductancewith realization of some but not all ofthe advantages attained when theinductance is used.

The insulating spacers 26 supported by cylinder I6 in turn supportauxiliary dipole elements 28,

" each capacitively coupled at its opposite ends 3l! to the transmissionline I8 through the capacitance between the ends of the auxiliary dipoleand the adjacent main dipole elements I2 and I4 respectively.

Though, as in Fig. l, the main dipole elements maybe somewhat conical inshape, they may be of practically any cross sectional form provided theaverage transverse section is sufciently great to obtain a low Q," andto enable adequate capacitive coupling at points 30. If desired, forexample, the antenna elements may each be formed in the shape of a rightcircular cylinder, or may be of diamond or elliptical vertical section:preferably, as in later embodiments exemplied by Figs. 6, 7 and 8, theymay be wide flat strips.

Though the auxiliary dipoles 28 are preferably longitudinal stripconductors, as shown in this and other modifications of the invention,they may be of other physical shape. The strips 28, Fig. 2, may beincreased in width circumferentially of the main dipole elements ifdesired. It is also possible to use but one auxiliary dipole 28 or toreplace all of them by a cylindrical conductor of the same lengthdisposed concentrically about the main dipole elements I2 and I4. Theband-pass characteristics of the antenna may be varied by bending theends of dipoles 28 toward or away from the main dipole I to increase ordecrease the capacity coupling between them.

For use in transmission, excitation is appliedv to the antenna throughthe transmission line I8. Assuming the excitation frequency is in theneighborhood of the natural or fundamental resonant frequency of dipoleI8, it will radiate but since this frequency is much lower than thenatural frequency of the auxiliary dipoles, they produce very littleradiation at such frequency. However, because the dipoles 28 arecapacitively coupled to both of the radiating elements I2 and I 4 thecapacitance between the latter is effectively increased and theresonance band of dipole III is effectively widened.

Assuming now the excitation frequency is much higher (approximately thenatural or fundamental frequency of the auxiliary dipoles 28), the maindipole I Il produces very little radiation; however, the auxiliarydipoles 28, each excited through the capacitance at points 38, produceconsiderable radiation at such high frequency.

At all frequencies intermediate their natural frequencies, the dipolesI0 and 28 act in supplementary manner to produce satisfactory radiationor absorption characteristics of the composite antenna formed by them,and in fact, as later discussed in connection with Fig. 3, the antennasystem of Fig. 1 has very satisfactory characteristics considerablybelow the natural frequency of dipole I8 and considerably above thenatural frequency of dipole 28.

In one physical embodiment or Fig. l, the overall length A of the maindipole I8 was approximately 42 inches, the length of each auxiliarydipole was approximately 17 inches and the maximum diameter C of eachmain dipole element was approximately 8 inches. The antenna sodimensioned had satisfactory radiation characteristics throughout therange of from 100 megacycles, to 300 megacycles which covers 4a largenumber of channels assigned to public, private and government servicesfor many uses including television broadcast, frequency-modulatedbroadcast, and point to point communications.A It should be noted theratio of the terminal frequencies of this band is 3 to 1, whereas withprevious so-called broad-band antennas the ratio of terminal frequencieswas at best only about 1.25 or 1.5 to 1 and that obtainable only byrecourse to dipole elements of excessively large cross-sectionaldimensions, prohibitive, on shipboard for example, where space is at apremium and in all cases creating difficult mounting and constructionproblems. It should further be noted that the operating range of suchprevious so-called broad-band antennas did not extend through anyharmonic or multiple resonance frequency of the antenna.

An antenna constructed in accordance with the invention is notdimensionally critical: that is, the shape and size of the dipoleelements may be varied Within reasonable limits without adverselyaifecting the radiation or absorption characteristics which canbeadjusted for attainment of the desired band-pass by bending or deformingthe auxiliary dipoles or by changing the value of inductance 24.

For efficient transfer of energy between any antenna and the associatedtransmission line, the standing-wave-ratio, later herein defined, mustbe low and ideally is unity. However, an antenna is considered aneflicient radiator if the standingwave-ratio (SWR) does not exceed 2 or3 and as a satisfactory absorber if the standing-waveratio is not muchgreater than 5.

Fig. 3 is the SWR curve of an antenna constructed in accordance withFig. 1 and having the vdimensions above given. The main dipole I0 wasdimensioned to resonate at frequency f1, somewhat higher than megacyclesand the auxiliary dipoles 28 were dimensioned to resonate at frequencyf2 somewhat lower than 300 megacycles. As shown in Fig. 3, thestanding-waveratio, though varying within the limits 100 to 300megacycles, did not, at any frequency within those limits, exceed 2 anddid not exceed 5 throughout a much Wider range of frequencies extendingwell below 100 megacycles and substantially above 300 megacycles, Forthis curve, the characteristic impedance of the line I8 used with theantenna was about 50 ohms.

During either radiation, for transmission, or absorption, for reception,the antenna of Fig. l acts as, and may be considered the operatingequivalent of, a band-pass filter with broad-band characteristics. Thisis true not only of the particular construction shown in Fig. 1, but ofall modifications including those later herein disclosed and described.

The curve 34, Fig. 4, is exemplary of the reactive impedancecharacteristic of a dipole having small transverse cross section, forexample, a wire or rod of small diameter. At each of points 36 where thecurve 34 crosses the horizontal axis, the slope of the curve is steep,indicating sharp resonance. An antenna having such sharp resonance iswholly unsuited for efficient radiation at frequencies appreciablydisplaced from its fundamental resonant frequency because of theresulting large mismatch between its impedance and that of theassociated transmission line.

Broadening the dipole elements into a large surface of revolution, as inFig. 1, effects fiattening of the reactive impedance of the antenna',generally as shown by curve 38. The greatly decrease slope of curve 38at each of points 3B where the curvel crosses'the horizontal line (zeroreactance)l indicates a condition of substantial resonance exists over afairly broad band, insufficient, however, to attain the results heresought. The expedient of increasing the thickness or cross section of asingle dipole cannot, practicallyv be extended to attain band widths ofthe magnitude obtained by my composite antenna. By the further additionof capacitance by addition of the auxiliary dipoles 28 to the primarydipole ID, there is produced the characteristic curve 40, indicating myantenna, Fig. i. has net capacitive reactance throughout the frequencyrange of 100 to 300 megacycles, and that the magnitude of the changes inreactance throughout the range is very materially reduced.

Having in mind the composite antenna including the auxiliary dipoles andwidened main dipole has the frequency-reactance characteristicexemplified by curve 4i), the effect of the inductance 24 having therising frequency-reactance characteristic 42 is evident from Fig. 5. Itis pointed out the uncorrected antenna reactance characteristic 43,throughout a wide range of frequencies, closely approximates a mirrorimage or reflection of curve 42 about the horizontal axis. Consequently,Within that range and by'use of suitable inductance 24, the resultantantenna reactance is a nearly straight line 44 practically coincidentwith the horizontal axis; otherwise stated the antenna has very smallnet reactance throughout a broad frequency band. To attain thischaracteristic with the antenna constants above given, the coil 24 hadan inductance of about 0.3 microhenry.

' The inductance 24 may, as shown in Fig. 1, be connected across theterminals of the transmission line I8; to improve the symmetry when thetransmission line is, as preferably, of the concentric conductor typethe outer conductor 22 of the line may be connected to the center ofinductance 24, the other connections remaining unchanged.

Though the construction and operation of the antenna has been describedwith inductive reactance 24 connected between the main dipole elements,it has been found that a capacitive reactance, or condenser, may be soconnected in lieu of coil 24. The effect of such insertion upon a dipoleantenna having a characteristic such as exemplified by curve 38 of Fig.4 is to reduce the upper or positive peak value and, With addition ofauxiliary dipoles, the resultant characteristic will approximate curve4i). In other Words, the antenna reactance with a condenser substitutedfor coil 24 is low.

'From the foregoing, it is evident a broad band antenna need not havethe excessive dimensions otherwise required in absence of the capacitiveand radiating eiects of the auxiliary dipoles 28. Moreover and from amechanical standpoint, the antenna may be of simple durableconstruction, easily installed and can be manufactured inexpensively andwithoutv need to hold close tolerances.

The modification shown in Fig. 1 is disclosed inmy copending applicationSerial No. 622,657, now abandoned, of which this application is acontinuation in part.

Subsequent embodiments of the invention which are not only. of even lessexpensive and simpler construction but which still further and verymaterially increase the frequency coverage are shown in Figs. 6, 7 and8.

In the modification shown in Figs. 6 and 7, the main dipole IGAcomprises two elements I2A, I 4A each consisting of a wide flat strip ofaluminum or other suitable metal. The inductance per unit length of eachelement is low and the capacitance per unit length is high, i. e., theratio of inductance to capacitance per unit length is low. The Q of eachdipole is therefore low, for example, of the order of 5 and preferablymuch less. The two strips I2A, I4A are held in axial alignment by theirattachment to a strip or plate ISA of suitable insulating material. neartheir adjacent ends, the strips I2A and I4A are bent away from theirsupport IEA to afford capacitive coupling to the auxiliary dipole 28A.

In this modification, like that of Fig. 8 later described, the ends ofthe auxiliary dipole are well away from the main dipole so that ineffect each of the main ldipole elements I 2B, I4B is respectivelycoupled by capacity to an intermefdiate point of the overlying half ofthe auxiliary dipole. The band characteristic is generally that of vtwolow Q dipoles IBA, 28A which are parallel throughout (Fig. 6A), butinterconnected by' condensers K, K to points a and b' selected to obtaina satisfactory-impedance match between the antennav and lineat thehigher frequencies of the band for which the auxiliarydipole iseffective as a radiator or absorber.- The coupling capacities are alsosignificant at the lower frequencies of the band.y For example, the coil24A may be selected so that With these capacities it forms a loopcircuit which is resonant at about the frequency for which the maindipole exhibits fundamental resonance.. Therefore, at that'frequency,this loop circuit isthe equivalent of a very'high shunt impedance andthe rnain dipole consequently performs much as a'simple center-fedhalf-wave dipole. At lower and higher frequencies, this loop circuitexhibits inductive and capacitive reactance respectively so that themain dipole again becomes Yresonant at a frequency below its naturalfrequency and exhibits reduced impedance at frequencies above itsnatural frequency.

The auxiliary dipole 28A is also a wide strip of aluminum or othersuitable metal having small inductance and large capacitance per unitlength. It is supported centrally of the main dipole IA with itslongitudinal axis substantially in alignment with and parallel to theaxis of the main dipole by a Ametal bracket 26A which comprises twoU-shaped members respectively xedly attached to dipole 28A and thesupport ISA and adjustably attached to each other as by bolts 5U. Thewide faces of the strips I 2A, I4A and 28A are parallel to eachother-for large mutual coupling reactance of the dipoles.; vTheadjustment afforded by the split bracket permits variation of capacitivecoupling between the dipolesl in empirical attainment of the desiredband width. y The antenna assembly is supported by the mast 53,preferably tubular for enclosure of the transmission line. The mast maybe xedly or rotatably fastened at or nearV its base to a tower, roof,vehicle body or other-fixed or mobile structure. In this and othermodifications disclosed, the axis of the antenna may be vertical orhoi-il zontal in dependencev upon the polarization of the waves to betransmitted or received.

Preferably and as shown, the adjacent ends of the main dipole elementsIZA, I 4A are connected to an inductance 24A having generally thepurpose of coil 24 of Fig. 1. It is preferably included as one elementof the broad band-pass network N, Fig. 9, comprising the self and mutualreactances of the two dipoles and their effective resistances. As islater more fully discussed in connection with the quite similar antennaconstruction shown in Fig. 8, this network as seen by the transmissionline I8 is the equivalent of a reactance X and a resistance R in series,Fig'. 10. The eifective magnitude of the resistance R and the `magnitudeof the reactance X vary with frequency but the main and auxiliarydipoles are so dimensioned and coupled that the vector sum of theresistance and reactance remains quite constant throughout an extremelywide band of frequencies.

In the embodiment shown in Fig. 8, the main dipole IIIB comprises twowide strips I2B, I4B of suitable conductors affording a dipole having alow Q and an auxiliary dipole 28B, also a wide conductive strip toobtain a low Q. The auxili-` ary dipole f28B is supported by housing 26Bin that position with respect to the main dipole IUB which by virtue ofthe dimensions of the dipoles and the coupling between them affords thedesired band-pass characteristic'. For-that purpose, the housing 26B issuitably fastened to the supporting strip IBB of the main dipole. Thehousing 26B, preferably of good high-frequency insulating material, alsoforms an enclosure for the loading reactance 24B, and for theconnections of transmission line I8 to protect them from Weatherconditions otherwise temporarily or permanently affecting the operatingcharacteristics of the antenna.

Both the main dipole IDB and the auxiliary dipole 28B have smallinductance and large capacitance per unit length so that consideredindividually neither of them exhibits sharp resonance at any frequency.The complex network N, Fig. 9, formed by the self and mutual reactancesX1, X2 and X3X4 of the dipoles and their effective resistances R1, R2may be represented by an equivalent circuit, Fig. 10, comprisingreactance X and resistance R in series across the antenna end of thetransmission line I8. Thevmagnitudes of reactance X and resistance R aredifferent for different frequencies, but in accordance with thisinvention the reactance X is low for all frequencies within a very wideband and at each frequency within that band the magnitudes of reactanceand resistance are such that their vector sum closely approximates theirvector sum at al1 other frequencies within the aforesaid wide band. Thesignificant difference between the characteristics of my antenna system,Figs. 6, 7, 8, and that of the usual dipole can best be illustrated byspecific examples based on measurements.

Referring to Fig. 11, the dot-dash curve 34A is the frequency-reactancecurve of a dipole of 1% diameter copper tubing which is a halfwavelengthlong at a frequency of about 60 megacycles. As evident from the curve,within a frequency range of fromabout 40 to 200 megacycles, thereactance varies from well over 1000 Ohms (inductive) to well over 1000ohms (capacitive) and rapidly changes with frequency particularly in thevicinity of points 36A, 36B and 36C corresponding with frequencies ofabout 60, 120 and 180 megacycles respectively.

Within the range of 40 to 200 megacycles, the reactance of the dipoleswings back and forth in sign, that is. it changes to positive orinductive reactance from negative or capacitive reactance as thefrequency is increased from below to above about 60 megacycles, reversesback to capacitive reactance as the frequency is increased from below toabove 120 megacycles, and again shifts to inductive reactance as thefrequency shifts from below to above 180 megacycles. In other Words, theeffective reactance of the dipole changes sign, and changes rapidly inmagnitude, at frequencies corresponding with the fundamental andharmonic wavelengths of the dipole.

Furthermore, the effective resistance of the single thin dipole varieswidely over this same range of frequencies; as shown by curve 5I, Fig.l1, the effective resistance is low, less than 100 ohms, for frequenciesat which the antenna is a half-wavelength long, but is very high, about3,000 ohms, for frequencies at which the antenna is a full wavelengthlong.

. Still referring to Fig. 11, the solid line curve AOA is thefrequency-reactance curve of an antenna constructed in accordance withFig. 8 and having the following dimensions for service as a transmittingantenna in the frequency range of from about 40 to 200 megacycles: eachof the dipole elements IZB, I4B and 28B was a strip of aluminumone-eighth of an inch thick and four inches wide: the dimensions E and Fof .each main dipole element were 34 inches and 14 inches respectively:the length B of the auxiliary dipole was 28 inches: and the spacing Gwas 21/2 inches.

Throughout the range of frequencies from 4.0 to over 200 megacycles, theequivalent series reactance X of that antenna system as evident frominspection of curve 40A, was low and nowhere in that range variedrapidly. Moreover, the effective resistance R of that antenna system, asshown by curve 52, Fig. 11, was throughout that range of frequencies ofsuch magnitude at each frequency that the effect of the variations inreactance upon the effective antenna impedance was minimized. Thevariation in magnitude of the effective resistance with frequency is farless than the usual dipole throughout the frequency range of 40 to 200megacycles.

In brief, my antenna, system, and particularly as exemplified by Figs.6, 7 and 8 comprises multiple low Q dipoles of different lengths socoupled that their self impedances and mutual impedances form a network(1L, Fig. 9) which when reduced to its simple equivalent series circuit(Fig. 10) for each frequency will provide at the terminals of thetransmission line a low reactance X and a series resistance R of suchmagnitude that for al1 frequencies throughout an extremely wide range,the effective antenna impedance lkml will so closely match thecharacteristic impedance of the transmission line that thestand-Wave-ratio will be low throughout that wide range of frequencies.

The standlng-wave-ratio (SWR) may be dened as Zu=characteristicimpedance of transmission line R=equivalent series resistance of antenna(Fig.

X=equivalent series reactance of antenna (Fig.

By substitution in Equation 2 of the magnitudes of effective reactanceand resistance ascertainable from curves 40A and 52 of Fig. l1 for thefrequencies within the range of from 40 to over 200 megacycles, it isapparent the standing wave ratio is less than 3 when the characteristicimpedance of the transmission line is 300 ohms. This was verified byactual measurements which as plotted resulted in curve SWR of Fig. 12.This antenna system is therefore efficient for transmission at anyfrequency within the range of 40 to well over 200 megacycles; i. e.,over better than a 5 to l frequency coverage, and is eicient forreception over a much wider range.

Furthermore, and as evident from inspection of Figs. 13 to 15, thecharacteristic impedance of the transmission line I8 is not criticalwhen this antenna is used. Throughout the same extremely wide frequencyrange, the standing-Wave-ratio (SWR) is suitably loW, less than 3, whenthe antenna is used with transmission lines having impedances of 250,200 and ohms, and also, as can be veried, with higher and lowerimpedance lines although if the line impedance is too far above 300 ohmsor too' far below 150 ohms, the standing-waVe-ratio for this particularantenna will be excessive. v

From the generalrules above given, illustrated by specific example.those skilled in the'art may 'readily design and construct other broadband antennas suited individually to cover a wide range in this andother portions of the radio frequency spectrum and which throughout thatrange will satisfactorily match the characteristic impedance of theassociated transmission line.

The auxiliary dipole or dipoles not only provide for efficient radiationor absorption over a broad 'band of frequencies but may be dimensionedconcurrently to insure that throughout the band the field pattern isfree of nulls in the desired direction of reception or transmission. Forexample, with the particular composite antenna discussed in connectionwith Fig. l1, at each of various frequencies in the lower frequencyportion ofthe band, say from 4G to 100 rnegacycles, at which the main'dipole is primarily effective, the iieldpattern is approximately thesame as those of an ordinary dipole;that is', it has two lobes forming afigure eight, aifording best reception or transmission in aline ofdirection normal to the llongitudinal axis of the antenna.

4 At the higher frequencies of the range, the iield pattern of the maindipole, of and by itself, assumes different forms having marked nulls inthe desired direction of operation. For example, the field pattern ofthe main dipole at about 120 megacycles is a four-lobed, or clover-leafpattern exemplified by the broken line curve V of Fig. 16, havingwide,`deep nulls in both the Y and Z directions normal to the antennaaxis. Atl still higher frequencies, rsay about 200 megacycles, the iieldpattern of the main dipole is a six-lobed figure similar to curve V plustwo minor lobes normal to the line Y-Z.

At the higher frequencies, however, the auxiliary dipole becomesincreasingly effective so that its individual directional characteristicmodified that of the main dipole with the result that at all thehigherfrequencies at which undesirable the'desired line of direction Y-Z,whereas the 'main dipole itself, at that same frequency markedlydiscriminates against'reception or transmission in that same line ofdirection.

- Generally and in brief, the auxiliary' dipole not only providesv forproper matchingof the antenna and its transmission line over a widebandof frequencies, but also Acontrols the amplitudejand phaseof the currentin the main dipole, particularly at its harmonic frequencies,thus toprevent serious lobing and appearance of undesirable nulls in the iieldpattern at any lfrequency within :that wide band.

In 4view of the foregoing description of their dimensions, spacing andcharacteristics, the auxiliary dipoles'of` Figs. 1, 2, 6,'7 and 8Lshould not be confused with the directors or-reflectors'used "indirectionall antenna'arrays to attain enhanced directional selectivityat a particular frequency. In physical. and electrical length,directors' and reilectorsV differ only'afew per cent,"or lessQfromtheassociated driven dipole so thattheirindivid- "said band forY which'another of theln ex bits ual field patterns at t`different frequenciesand their individual frequency-reactance characteristics are practicallyidentical with those of the main dipole. Consequently, unlike theauxiliary dipoles of this invention, reflectors and'directors furtherincrease the sharpness-'of resonanceof the main dipole ands'o furtherreduce the already narrow frequency range in whichit can efficiently 'ina desired direction comprising mutually coupled low Q dipoles of suchsubstantially different length that they respectively exhibitfundamental resonance at frequencies whose ratioy is greater than 1.5,the fieldpatterns ofsaid dipoles-coni- 'plementarily combining at eachof all frequencies of the band in avoidance of 'nulls in -saidde'sireddirection and the self and mutual reactances of said dipoles combining`at each of all frequencies of the band to provide anequivalent'reactance which is low, said dipoles being spaced apart inparallel axial alignment to-permit capacitive coupling therebetween,anda transmission'lin'e corinected tothe center point of the longerdipoles;

2. A multi-channel broad-band antenna system for eicient transmission orreception in a desiredr direction and throughout a band the ratio ofwhose terminal frequencies is greater than-2 comprising mutually coupledlow Q dipoles having substantially different lengths, an insulatingsupport'between said dipoles for maintaining them in parallel axialalignment and capacitively coupled, said dipoles respectively exhibitingfundamental resonanceat frequencies corresponding `with said terminallfrequencies, the shapel and relative size of the field patterns of theindividual dipoles insuring the joint pattern at eachv of allfrequencies of the band shall be free of a null in said desireddirection, a transmission line connected to the center point of saidlonger dipole,

an inductance connected in parallel across said transmission line ofsufiicent magnitude' to com'- -pensatefor the capacitive reactance ofthe coupled dipoles substantially' through said band, the self andmutual impedances of said dipolesinsuring the effective impedance'oftheantenna system 'is for each frequency of said band the equivalent of areactance in series" with; a'resistancefsaid reactance andresistancebeing of such a'4 value that on a given'ftr'ansmission linethe standing- Wave-ratio'will below over a wide band of'frequencies. f ly A' y l 3. vA multi-channel broad-band antenna sys- `temforefiicienttranslnission'orlreception -in `a desired direction andthroughout aband'the ratio of whose terminal frequencies is'greater-than 2 comprising a pairV of mutually coupled lowjQ dipoles ofsubstantially different'lengths, an in'- sulating support between'saiddipoles for mailitainingthem in parallel axial alignment yandcapacitively coupled, one of said dipoles exhibitving fundamentalresonance at a frequncyin harr'nonic resonance in avoidance fnullsassures desired direction, and a. transmission line connected to thecenter point of said longer dipole for effecting interchange of energywith said dipoles, an inductance sufficient to compensate for thecapacitive reactance of said coupled dipoles connected in parallelacross said transmission line, the self and mutual impedances of saiddipoles forming a complex band-pass network whose series equivalent atlthe transmission line terminals appears at each frequency of said bandto be a. reactance in series with a resistance of such magnitude that,the standing-wave-ratio is not greater than 3 for transmission or 5 forreception.

4. A multi-channel broad-band antenna sysat a frequency substantiallythe said minimum frequency, a number of furtherAdipollescircumferentially arranged ,about said first dipole, said number offurther dipoles being greater than 2,

said further dipoles being shorter in length than Y said first dipoleand resonant at a frequency substantially the said maximum frequency,said further dipoles being capacitively coupled at their ends to areasintermediate the ends of the conductors of said rst dipole.

5. A multi-channel antenna system broadly. resonant over a band offrequencies the ratio of Whose terminal frequencies is greater than 1.5comprising a first center-fed dipole resonant-.Aat a frequency withinsaid range, a second end-fed dipole capacitively coupled to said firstdipole resonant at a substantially different frequency within saidrange, and inductance connected to the center of said first dipole ofmagnitude to compensate for capacitive reactance of the cou*- pleddipoles substantially throughout said band.

`6. A multi-channel broad-band antenna system comprising a first dipoleconsisting of a rst radiating element of large transverse cross sectionand a second radiating element of large transverse cross section inaxially-abutting relation, an insulating support joining said radiatingelements, a plurality of shorter dipoles mounted on said supportcircumferentially and equally spaced about said radiating elements, atransmission line connected to the rst and second radiating elements attheir abutting ends, and inductance connected across said transmissionline in parallel with said radiating elements, the ends f said pluralityof shorter dipoles being in cap'acitively-coupled i relationrespectively ywith areas intermediate the remote ends of said radiatingelements and co'acting therewith 'to' provide lfor low net reactance ofthe antenna system over a band of frequencies whose maximum fre-A quencyto minimum frequency is 'greater'than 1.5.

7. A multi-channel antenna system comprising a plurality ofVcooperatively associated main and auxiliary low Q dipoles ofsubstantially different length and maintained in parallel axialalignment, said dipole being of large transverse 'cross-section and saidauxiliary dipoles being a plurality of shorter dipoles placedvcircumferentially and equally spaced around the large main dipole vandcapacitively coupled thereto at their ends, a transmission lineconnected to the center of said main dipole, and a lumped inductance atthe center of said main dipole connected in 'par- 'allei thereto acrosssaid transmission line, 'there- 'actances of all of said dipolescooperating to pro'- 'duce' a substantially resonant 'condition through-12 v out a wide band of frequencies the ratio of whose terminalfrequencies is greater than 2.

8. A multi-channel transmitting-receiving an'- tenna constructionforming a band-pass network comprising main and auxiliary low Q dipolesof substantially different length and maintained in parallel alignment,said dipoles being flat strips whose inductances per unit length aresmall and whose capacities per unit length are large, a transmissionline connected to the center of one of said dipoles, lumped inductanceat the center of one of said dipoles connected in parallel theretoacross said transmission line, the ends of the auxiliary dipole beingcapacitivity coupled to the main dipole, all of said reactancescooperating to produce a substantially resonant condition throughout awide band of frequencies, the ratio of Whose terminal frequencies isgreater than 2.

9. A multi-channel antenna system broadly resonant throughout a band offrequencies the ratio of whose maximum frequency to minimum frequency isgreater than 1.5 comprising a pair of low Q dipoles o f substantiallydifferent physical and electrical lengths, an insulating support betweensaid dipoles for maintaining parallel alignment so that said dipoles arecapacitively coupled, a transmission line center feeding one of saiddipoles, and lumped inductance connected across said transmission line,said different lengths of said dipoles respectively corresponding withsubstantially different resonant frequencies within said band and havinglsuch individual and mutual reactances that said system exhibits low netreactance throughout said band.

10. A multi-channel antenna system broadly resonant throughout a band offrequencies the ratio of whose maximum frequency to minimum frequency isgreater than 1.5 comprising dipoles individually resonant atsubstantially different frequencies, said dipoles being of substantiallydifferent length and positioned for capacitive coupling therebetween, atransmission line for center-feeding one of said dipoles, and inductanceof magnitude to compensate for capacitive react'- ance of the coupleddipoles substantially throughout said band connected to saidtransmission line, said dipoleshaving such individual and mutualreactances that said system exhibits low and capacitive reactancethroughout said band of frequencies.

11. A multi-channel antenna system broadly resonant throughout a band offrequencies the ratio of whose maximum frequency to minimum frequency isgreater than 1.5 comprising dipoles individually resonant atsubstantially different different length and positioned for' capacitivecoupling therebetween, a transmission line for center-feeding one ofsaid dipoles, said dipoles having such individual and mutual -reactancesthat saidsystem exhibits low and capacitive 'reactance throughoutsaid'band of frequencies, and lumped inductance at the center of oneI ofsaid dipoles connected in parallel across said transmission linecompensating for said low capacitive reactance.

12. A broad-band antenna for efficient transmission or receptionthroughout said band 'comprising a pair of axially aligned broad stripsforming a center-fed dipole, and a second shorter dipole exhibitingfundamental resonance at a'fre'- quency within said band fr whichsaid'first- 'named dipole exhibits harmonics resonance, saidsecond-named 'dipole comprising a broad'st'rip assonos having its wideface parallel to and spaced from the wide faces of said pair of stripsto provide mutual capacitive reactance which with the selfreactances ofthe dipoles insures low eifective reactance at the center of saidfirst-named dipole at all frequencies within said band.

13. A broad-band antenna comprising a pair of broad strips forming a lowQ center-fed dipole, a transmission line connected to adjacent ends ofsaid strips, an insulating support mechanically connecting said stripsin axial alignment, an insulating housing on said support and enclosingsaid ends of said strips and the transmission line connections thereto,and a second shorter low Q dipole comprising a broad` strip supported bysaid housing with its wide face parallel to the Wide faces of said pairof strips to provide capac itive coupling thereto.

14. A broad-band antenna system affording a standing-Wave-ratio notgreater' than 2 over a frequency band the ratio of whose maximumfrequency to minimum frequency is greater than 1.5 comprising a rstcenter-fed dipole having an inductance connected at its center inparallel across the feed line, a plurality of shorter dipoles placedcircumferentially and equally spaced about said rst dipole in parallelaxial alignment therewith, said shorter dipoles being capacitivelycoupled to said first dipole at their ends. said rst dipole being oflength for acting as the primary radiator at the lower frequencies ofsaid band and said shorter dipoles acting as the primary radiators atthe higher frequencies of said band.

15. A broad-band antenna system comprising a first center-fed dipole oflarge average transverse cross section and having an inductanceconnected at is center across the feed line, a'plurality of shorterdipoles positioned circumferentially about said iirst dipole, saidshorter dipoles arranged about said first dipole in spaced parallelrelation and capacitively coupled therewith to provide for low netreactance of said system throughout a band of frequencies thev ratio ofwhose maximum frequency to minimum frequency is greater than 1.5.

i FREDERICK A. KOLSTER.

REFERENCES CITED The following references are of record in the file ofthis patent: i.

UNITED STATES PATENTS Number Name "Date 2,044,779, Hanson June 23, 19362,188,389; Cork et al. `Jan. 30, 1940 2,192,532 Katzin Mar. 5,19402,268,640' Brown Jan. 6, 1942 2,287,220 Alford June 23, 1942 2,289,856-Alford July 14, 1942 2,297,329 Scheldorf Sept; 29, 1942 2,311,364'Buschbeck et al. Feb. 16, 1943 2,380,333 Scheldorf July l0, 1945 IFOREIGN PATENTS Number Country Date 879,230 France Nov. 10, 1942

